US8747400B2 - Systems and methods for screen electrode securement - Google Patents

Abstract

Systems and methods for securing a screen-type active electrode to the distal tip of an electrosurgical device used for selectively applying electrical energy to a target location within or on a patient's body. A securing electrode is disposed through the screen electrode and mechanically joined to an insulative support body while also creating an electrical connection and mechanical engagement with the screen electrode. The electrosurgical device and related methods are provided for resecting, cutting, partially ablating, aspirating or otherwise removing tissue from a target site, and ablating the tissue in situ. The present methods and systems are particularly useful for removing tissue within joints, e.g., synovial tissue, meniscus, articular cartilage and the like.

Description

FIELD OF THE INVENTION

The present invention relates generally to the field of electrosurgery, and more particularly to apparatus and methods for applying high frequency voltage to ablate tissue. More particularly, the present invention relates to apparatus and methods for securing a substantially flat screen-type active electrode to the distal tip of the shaft of an electrosurgical instrument.

BACKGROUND OF THE INVENTION

Conventional electrosurgical methods are widely used since they generally achieve hemostasis and reduce patient bleeding associated with tissue cutting operations while improving the surgeon's visibility of the treatment area. Many of the electrosurgical devices used in electrosurgery make use of a screen-type active electrode which is typically cut, or etched, from a sheet of conductive material. These electrosurgical devices and procedures, however, suffer from a number of disadvantages. For example, screen-type active electrodes typically require some method of securement to an insulative body and furthermore to the distal tip of the device itself. Failure to adequately secure the screen electrode to the insulative body may result in improper device function and possible patient harm during the electrosurgical procedure.

Prior attempts to secure the screen active electrode to the insulative body have involved mechanical, thermal, and chemical means or various combinations thereof. Numerous mechanical forms of securement have been utilized, while adhesives have been used as a chemical form of joining, and welding the screen may provide one thermal method of joining. These mechanical joining methods may also include the use of plastic, or non-recoverable, deformations of the materials being used for securement. However, even in combination with other joining methods, the above-listed methods for fixation provide only marginally effective solutions that typically are challenged over extended periods of use.

Accordingly, devices and methods which allow for the securement of flat screen active electrodes to the insulative body of an electrosurgical instrument while maintaining electrical connections through the insulative body are desired. In particular, mechanical methods for providing reasonable and durable securement of an electrically connected screen active electrode to the insulative body at the distal tip of an electrosurgical device while providing enhanced electrosurgical operating parameters are desired.

SUMMARY OF THE INVENTION

The present invention provides systems, apparatus and methods for mechanically securing a screen type active electrode to the insulative body at the distal tip of an electrosurgical device. In particular, methods and apparatus are provided for reliably securing the screen electrode over extended periods of use. Further, the methods and systems of the present invention are particularly useful for providing expanded and enhanced electrosurgical operating parameters.

In one aspect of the invention, the method of securement comprises inserting a securing electrode through a channel or slot in both the screen electrode and insulative body. In a configuration where the screen electrode is supported by the insulative body, the securing electrode functions to mechanically couple the screen electrode to the insulative body, and also functions to electrically couple the screen electrode to a high frequency power supply via electrical connectors. The securing electrode may be characterized by extended leg portions having tabs at one end that engage or interfere with the channel in the insulative body, thereby preventing axial movement of the securing electrode. Thus, the securing electrode provides a mechanical method of joining the screen electrode to the insulative body while also providing an electrical connection to transmit RF energy through the insulative body to the screen electrode.

Another configuration of the electrosurgical device according to the present disclosure comprises an active screen electrode having at least two bilateral channels therethrough. At least two bilateral securing electrodes are provided and are respectively inserted through the channels of the screen electrode. Additionally, the device comprises an insulative support member having at least two bilateral channels correspondingly positioned with regard to the screen electrode channels. The bilateral securing electrodes are inserted through the support member and screen electrode channels and may be oriented symmetrically to thereby allow for creation of a zone for RF ablation between the two securing electrodes. Further, the bilateral screen electrodes each have a leg portion with a tab at one end, wherein the tab slides into a locked position within the support member to secure the screen electrode in place.

In certain configurations, the securing electrodes may be characterized by a saw tooth pattern on a superior surface. Additionally, the securing electrodes may be formed in the shape of a staple or bridge, thereby allowing for the creation of another zone of RF ablation in a space between the staple securing electrode and the screen electrode. The added edges formed on the securing electrode in these configurations may result in increased current density and thus promote the formation of improved zones of RF ablation.

In yet another configuration, the active electrode comprises a conductive screen having a plurality of holes and is positioned over the insulative body at the distal tip of an electrosurgical device in relation to the distal opening of an aspiration lumen. In the representative embodiment, the screen electrode is supported by the insulating support member such that the one of the plurality of holes on the screen is aligned with the aspiration lumen opening, thereby allowing for the aspiration of unwanted tissue and electrosurgery byproducts from the target site. Additionally, the screen and the distal opening of the aspiration lumen may be positioned on a lateral side of the instrument (i.e., facing 90 degrees from the instrument axis).

In open procedures, the system may further include a fluid delivery element for delivering electrically conducting fluid to the active electrode(s) and the target site. The fluid delivery element may be located on the instrument, e.g., a fluid lumen or tube, or it may be part of a separate instrument. Alternatively, an electrically conducting gel or spray, such as a saline electrolyte or other conductive gel, may be applied to the tissue. In addition, in arthroscopic procedures, the target site will typically already be immersed in a conductive irrigant, i.e., saline. In these embodiments, the apparatus may not have a fluid delivery element. In both embodiments, the electrically conducting fluid will preferably provide a current flow path between the active electrode terminal(s) and the return electrode(s). In an exemplary embodiment, a return electrode is located on the instrument and spaced a sufficient distance from the active electrode terminal(s) to substantially avoid or minimize current shorting therebetween and to isolate the return electrode from tissue at the target site.

In another aspect of the invention, a method comprises positioning one or more active electrode(s) (which may include an active screen electrode and securing electrode) at the target site within a patient's body and applying a suction force to a tissue structure to draw the tissue structure to the active electrode(s). High frequency voltage is then applied between the active electrode(s) and one or more return electrode(s) to ablate the tissue structure. Typically, the tissue structure comprises a flexible or elastic connective tissue, such as synovial tissue. This type of tissue is typically difficult to remove with conventional mechanical and electrosurgery techniques because the tissue moves away from the instrument and/or becomes clogged in the rotating cutting tip of the mechanical shaver or microdebrider. The present invention, by contrast, draws the elastic tissue towards the active electrodes, and then ablates this tissue with the mechanisms described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electrosurgical system incorporating a power supply and an electrosurgical probe;

FIG. 2 is a perspective view of another electrosurgical system incorporating a power supply, an electrosurgical probe and a supply of electrically conductive fluid for delivering the fluid to the target site;

FIG. 3 is a side view of an electrosurgical probe for ablating and removing tissue;

FIG. 4 is a cross-sectional view of the electrosurgical probe ofFIG. 3;

FIG. 5 illustrates a detailed view illustrating ablation of tissue;

FIG. 6 is an enlarged detailed view of the distal end portion of an embodiment of the probe ofFIG. 3;

FIGS. 7A and 7B are detailed view of the securing electrode and screen electrode utilized in the electrosurgical probe ofFIG. 6;

FIG. 8 is an exploded view of the distal end portion of the probe ofFIG. 6;

FIG. 9 is a perspective view of the distal end portion of the probe ofFIG. 6; and

FIG. 10 is a perspective view of the securing electrodes and screen electrode.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides systems and methods for selectively applying electrical energy to a target location within or on a patient's body. The present invention is particularly useful in procedures where the tissue site is flooded or submerged with an electrically conducting fluid, such as arthroscopic surgery of the knee, shoulder, ankle, hip, elbow, hand or foot. In other procedures, the present invention may be useful for collagen shrinkage, ablation and/or hemostasis in procedures for treating target tissue alone or in combination with the volumetric removal of tissue. More specifically, the embodiments described herein provide for electrosurgical devices characterized by a substantially flat screen active electrode disposed at the distal tip of the device. Additionally, the present embodiments include apparatus and methods for the mechanical securement of the screen electrode to the insulative body located at the distal tip of the device. Such methods of mechanical securement of the screen electrode may extend the operating period of the electrosurgical device by providing a more secure method of attachment.

Before the present invention is described in detail, it is to be understood that this invention is not limited to particular variations set forth herein as various changes or modifications may be made to the invention described and equivalents may be substituted without departing from the spirit and scope of the invention. As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process act(s) or step(s) to the objective(s), spirit or scope of the present invention. All such modifications are intended to be within the scope of the claims made herein.

Methods recited herein may be carried out in any order of the recited events which is logically possible, as well as the recited order of events. Furthermore, where a range of values is provided, it is understood that every intervening value, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the invention. Also, it is contemplated that any optional feature of the inventive variations described may be set forth and claimed independently, or in combination with any one or more of the features described herein.

All existing subject matter mentioned herein (e.g., publications, patents, patent applications and hardware) is incorporated by reference herein in its entirety except insofar as the subject matter may conflict with that of the present invention (in which case what is present herein shall prevail). The referenced items are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such material by virtue of prior invention.

Reference to a singular item, includes the possibility that there are plural of the same items present. More specifically, as used herein and in the appended claims, the singular forms “a,” “an,” “said” and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation. Last, it is to be appreciated that unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

The electrosurgical device of the present embodiments may have a variety of configurations as described above. However, at least one variation of the embodiments described herein employs a treatment device using Coblation® technology.

As stated above, the assignee of the present invention developed Coblation® technology. Coblation® technology involves the application of a high frequency voltage difference between one or more active electrode(s) and one or more return electrode(s) to develop high electric field intensities in the vicinity of the target tissue. The high electric field intensities may be generated by applying a high frequency voltage that is sufficient to vaporize an electrically conductive fluid over at least a portion of the active electrode(s) in the region between the tip of the active electrode(s) and the target tissue. The electrically conductive fluid may be a liquid or gas, such as isotonic saline, blood, extracelluar or intracellular fluid, delivered to, or already present at, the target site, or a viscous fluid, such as a gel, applied to the target site.

When the conductive fluid is heated enough such that atoms vaporize off the surface faster than they recondense, a gas is formed. When the gas is sufficiently heated such that the atoms collide with each other causing a release of electrons in the process, an ionized gas or plasma is formed (the so-called “fourth state of matter”). Generally speaking, plasmas may be formed by heating a gas and ionizing the gas by driving an electric current through it, or by shining radio waves into the gas. These methods of plasma formation give energy to free electrons in the plasma directly, and then electron-atom collisions liberate more electrons, and the process cascades until the desired degree of ionization is achieved. A more complete description of plasma can be found in Plasma Physics, by R. J. Goldston and P. H. Rutherford of the Plasma Physics Laboratory of Princeton University (1995), the complete disclosure of which is incorporated herein by reference.

As the density of the plasma or vapor layer becomes sufficiently low (i.e., less than approximately 1020 atoms/cm3 for aqueous solutions), the electron mean free path increases to enable subsequently injected electrons to cause impact ionization within the vapor layer. Once the ionic particles in the plasma layer have sufficient energy, they accelerate towards the target tissue. Energy evolved by the energetic electrons (e.g., 3.5 eV to 5 eV) can subsequently bombard a molecule and break its bonds, dissociating a molecule into free radicals, which then combine into final gaseous or liquid species. Often, the electrons carry the electrical current or absorb the radio waves and, therefore, are hotter than the ions. Thus, the electrons, which are carried away from the tissue towards the return electrode, carry most of the plasma's heat with them, allowing the ions to break apart the tissue molecules in a substantially non-thermal manner.

By means of this molecular dissociation (rather than thermal evaporation or carbonization), the target tissue structure is volumetrically removed through molecular disintegration of larger organic molecules into smaller molecules and/or atoms, such as hydrogen, oxygen, oxides of carbon, hydrocarbons and nitrogen compounds. This molecular disintegration completely removes the tissue structure, as opposed to dehydrating the tissue material by the removal of liquid within the cells of the tissue and extracellular fluids, as is typically the case with electrosurgical desiccation and vaporization. A more detailed description of these phenomena can be found in commonly assigned U.S. Pat. No. 5,697,882 the complete disclosure of which is incorporated herein by reference.

In some applications of the Coblation® technology, high frequency (RF) electrical energy is applied in an electrically conducting media environment to shrink or remove (i.e., resect, cut, or ablate) a tissue structure and to seal transected vessels within the region of the target tissue. Coblation® technology is also useful for sealing larger arterial vessels, e.g., on the order of about 1 mm in diameter. In such applications, a high frequency power supply is provided having an ablation mode, wherein a first voltage is applied to an active electrode sufficient to effect molecular dissociation or disintegration of the tissue, and a coagulation mode, wherein a second, lower voltage is applied to an active electrode (either the same or a different electrode) sufficient to heat, shrink, and/or achieve hemostasis of severed vessels within the tissue.

The amount of energy produced by the Coblation® device may be varied by adjusting a variety of factors, such as: the number of active electrodes; electrode size and spacing; electrode surface area; asperities and sharp edges on the electrode surfaces; electrode materials; applied voltage and power; current limiting means, such as inductors; electrical conductivity of the fluid in contact with the electrodes; density of the fluid; and other factors. Accordingly, these factors can be manipulated to control the energy level of the excited electrons. Since different tissue structures have different molecular bonds, the Coblation® device may be configured to produce energy sufficient to break the molecular bonds of certain tissue but insufficient to break the molecular bonds of other tissue. For example, fatty tissue (e.g., adipose) has double bonds that require an energy level substantially higher than 4 eV to 5 eV (typically on the order of about 8 eV) to break. Accordingly, the Coblation® technology generally does not ablate or remove such fatty tissue; however, it may be used to effectively ablate cells to release the inner fat content in a liquid form. Of course, factors may be changed such that these double bonds can also be broken in a similar fashion as the single bonds (e.g., increasing voltage or changing the electrode configuration to increase the current density at the electrode tips). A more complete description of these phenomena can be found in commonly assigned U.S. Pat. Nos. 6,355,032, 6,149,120 and 6,296,136, the complete disclosures of which are incorporated herein by reference.

The active electrode(s) of a Coblation® device may be supported within or by an inorganic insulating support member positioned near the distal end of the instrument shaft. The return electrode may be located on the instrument shaft, on another instrument or on the external surface of the patient (i.e., a dispersive pad). The proximal end of the instrument(s) will include the appropriate electrical connections for coupling the return electrode(s) and the active electrode(s) to a high frequency power supply, such as an electrosurgical generator.

Further discussion of applications and devices using Coblation® technology may be found as follows. Issued U.S. Pat. Nos. 6,296,638; and 7,241,293 both of which are incorporated by reference. Pending U.S. application Ser. No. 11/612,995 filed Dec. 19, 2006, which is incorporated by reference.

In one example of a Coblation® device for use with the presently-described embodiments, the return electrode of the device is typically spaced proximally from the active electrode(s) a suitable distance to avoid electrical shorting between the active and return electrodes in the presence of electrically conductive fluid. In many cases, the distal edge of the exposed surface of the return electrode is spaced about 0.5 mm to 25 mm from the proximal edge of the exposed surface of the active electrode(s), preferably about 1.0 mm to 5.0 mm. Of course, this distance may vary with different voltage ranges, conductive fluids, and depending on the proximity of tissue structures to active and return electrodes. The return electrode will typically have an exposed length in the range of about 1 mm to 20 mm.

A Coblation® treatment device for use according to the present descriptions may use a single active electrode or an array of active electrodes spaced around the distal surface of a catheter or probe. In the latter embodiment, the electrode array usually includes a plurality of independently current-limited and/or power-controlled active electrodes to apply electrical energy selectively to the target tissue while limiting the unwanted application of electrical energy to the surrounding tissue and environment resulting from power dissipation into surrounding electrically conductive fluids, such as blood, normal saline, and the like. The active electrodes may be independently current-limited by isolating the terminals from each other and connecting each terminal to a separate power source that is isolated from the other active electrodes. Alternatively, the active electrodes may be connected to each other at either the proximal or distal ends of the catheter to form a single wire that couples to a power source.

In certain configurations, each individual active electrode in the electrode array may be electrically insulated from all other active electrodes in the array within the instrument and is connected to a power source which is isolated from each of the other active electrodes in the array or to circuitry which limits or interrupts current flow to the active electrode when low resistivity material (e.g., blood, electrically conductive saline irrigant or electrically conductive gel) causes a lower impedance path between the return electrode and the individual active electrode. The isolated power sources for each individual active electrode may be separate power supply circuits having internal impedance characteristics which limit power to the associated active electrode when a low impedance return path is encountered. By way of example, the isolated power source may be a user selectable constant current source. In this embodiment, lower impedance paths will automatically result in lower resistive heating levels since the heating is proportional to the square of the operating current times the impedance. Alternatively, a single power source may be connected to each of the active electrodes through independently actuatable switches, or by independent current limiting elements, such as inductors, capacitors, resistors and/or combinations thereof. The current limiting elements may be provided in the instrument, connectors, cable, controller, or along the conductive path from the controller to the distal tip of the instrument. Alternatively, the resistance and/or capacitance may occur on the surface of the active electrode(s) due to oxide layers which form selected active electrodes (e.g., titanium or a resistive coating on the surface of metal, such as platinum).

The Coblation® device is not limited to electrically isolated active electrodes, or even to a plurality of active electrodes. For example, in certain embodiments the array of active electrodes may be connected to a single lead that extends through the catheter shaft to a power source of high frequency current.

The voltage difference applied between the return electrode(s) and the active electrode(s) will be at high or radio frequency, typically between about 5 kHz and 20 MHz, usually being between about 30 kHz and 2.5 MHz, preferably being between about 50 kHz and 500 kHz, often less than 350 kHz, and often between about 100 kHz and 200 kHz. In some applications, applicant has found that a frequency of about 100 kHz is useful because the tissue impedance is much greater at this frequency. In other applications, such as procedures in or around the heart or head and neck, higher frequencies may be desirable (e.g., 400-600 kHz) to minimize low frequency current flow into the heart or the nerves of the head and neck.

The RMS (root mean square) voltage applied will usually be in the range from about 5 volts to 1000 volts, preferably being in the range from about 10 volts to 500 volts, often between about 150 volts to 400 volts depending on the active electrode size, the operating frequency and the operation mode of the particular procedure or desired effect on the tissue (i.e., contraction, coagulation, cutting or ablation).

Typically, the peak-to-peak voltage for ablation or cutting with a square wave form will be in the range of 10 volts to 2000 volts and preferably in the range of 100 volts to 1800 volts and more preferably in the range of about 300 volts to 1500 volts, often in the range of about 300 volts to 800 volts peak to peak (again, depending on the electrode size, number of electrons, the operating frequency and the operation mode). Lower peak-to-peak voltages will be used for tissue coagulation, thermal heating of tissue, or collagen contraction and will typically be in the range from 50 to 1500, preferably 100 to 1000 and more preferably 120 to 400 volts peak-to-peak (again, these values are computed using a square wave form). Higher peak-to-peak voltages, e.g., greater than about 800 volts peak-to-peak, may be desirable for ablation of harder material, such as bone, depending on other factors, such as the electrode geometries and the composition of the conductive fluid.

As discussed above, the voltage is usually delivered in a series of voltage pulses or alternating current of time varying voltage amplitude with a sufficiently high frequency (e.g., on the order of 5 kHz to 20 MHz) such that the voltage is effectively applied continuously (as compared with, e.g., lasers claiming small depths of necrosis, which are generally pulsed about 10 Hz to 20 Hz). In addition, the duty cycle (i.e., cumulative time in any one-second interval that energy is applied) is on the order of about 50% for the present invention, as compared with pulsed lasers which typically have a duty cycle of about 0.0001%.

The preferred power source of the present invention delivers a high frequency current selectable to generate average power levels ranging from several milliwatts to tens of watts per electrode, depending on the volume of target tissue being treated, and/or the maximum allowed temperature selected for the instrument tip. The power source allows the user to select the voltage level according to the specific requirements of a particular neurosurgery procedure, cardiac surgery, arthroscopic surgery, dermatological procedure, ophthalmic procedures, open surgery or other endoscopic surgery procedure. For cardiac procedures and potentially for neurosurgery, the power source may have an additional filter, for filtering leakage voltages at frequencies below 100 kHz, particularly voltages around 60 kHz. Alternatively, a power source having a higher operating frequency, e.g., 300 kHz to 600 kHz may be used in certain procedures in which stray low frequency currents may be problematic. A description of one suitable power source can be found in commonly assigned U.S. Pat. Nos. 6,142,992 and 6,235,020, the complete disclosure of both patents are incorporated herein by reference for all purposes.

The power source may be current limited or otherwise controlled so that undesired heating of the target tissue or surrounding (non-target) tissue does not occur. In a presently preferred embodiment of the present invention, current limiting inductors are placed in series with each independent active electrode, where the inductance of the inductor is in the range of 10 uH to 50,000 uH, depending on the electrical properties of the target tissue, the desired tissue heating rate and the operating frequency. Alternatively, capacitor-inductor (LC) circuit structures may be employed, as described previously in U.S. Pat. No. 5,697,909, the complete disclosure of which is incorporated herein by reference. Additionally, current-limiting resistors may be selected. Preferably, these resistors will have a large positive temperature coefficient of resistance so that, as the current level begins to rise for any individual active electrode in contact with a low resistance medium (e.g., saline irrigant or blood), the resistance of the current limiting resistor increases significantly, thereby minimizing the power delivery from said active electrode into the low resistance medium (e.g., saline irrigant or blood).

Referring now toFIG. 1, an exemplary electrosurgical system for resection, ablation, coagulation and/or contraction of tissue will now be described in detail. As shown, certain embodiments of the electrosurgical system generally include anelectrosurgical probe20 connected to apower supply10 for providing high frequency voltage to one or more electrode terminals onprobe20.Probe20 includes aconnector housing44 at its proximal end, which can be removably connected to aprobe receptacle32 of aprobe cable22. The proximal portion ofcable22 has aconnector34 tocouple probe20 topower supply10 atreceptacle36.Power supply10 has an operator controllablevoltage level adjustment38 to change the applied voltage level, which is observable at avoltage level display40.Power supply10 also includes one ormore foot pedals24 and acable26 which is removably coupled to areceptacle30 with acable connector28. Thefoot pedal24 may also include a second pedal (not shown) for remotely adjusting the energy level applied toelectrode terminals42, and a third pedal (also not shown) for switching between an ablation mode and a coagulation mode.

Referring now toFIG. 2, anexemplary electrosurgical system211 for treatment of tissue in ‘dry fields’ will now be described in detail. Of course,system211 may also be used in ‘wet field’, i.e., the target site is immersed in electrically conductive fluid. However, this system is particularly useful in ‘dry fields’ where the fluid is preferably delivered through electrosurgical probe to the target site. As shown,electrosurgical system211 generally comprises an electrosurgical handpiece or probe210 connected to apower supply228 for providing high frequency voltage to a target site and afluid source221 for supplying electrically conductingfluid250 to probe210. Thesystem211 may also include a vacuum source (not shown) for coupling to a suction lumen disposed in probe210 (not shown) via a connection tube (not shown) onprobe210 for aspirating the target site, as discussed below in more detail.

As shown, probe210 generally includes aproximal handle219 and anelongate shaft218 having anarray212 ofelectrode terminals258 at its distal end. A connectingcable234 has aconnector226 for electrically coupling theelectrode terminals258 topower supply228. Theelectrode terminals258 are electrically isolated from each other and each of theterminals258 is connected to an active or passive control network withinpower supply228 by means of a plurality of individually insulated conductors (not shown). Afluid supply tube215 is connected to afluid tube214 ofprobe210 for supplying electrically conductingfluid250 to the target site.

Similar to the above embodiment shown inFIG. 1,power supply228 has an operator controllablevoltage level adjustment230 to change the applied voltage level, which is observable at avoltage level display232.Power supply228 also includes first, second andthird foot pedals237,238,239 and acable236 which is removably coupled topower supply228. Thefoot pedals237,238,239 allow the surgeon to remotely adjust the energy level applied toelectrode terminals258. In an exemplary embodiment,first foot pedal237 is used to place the power supply into the “ablation” mode andsecond foot pedal238places power supply228 into the “coagulation” mode. Thethird foot pedal239 allows the user to adjust the voltage level within the “ablation” mode. In the ablation mode, a sufficient voltage is applied to the electrode terminals to establish the requisite conditions for molecular dissociation of the tissue (i.e., vaporizing a portion of the electrically conductive fluid, ionizing charged particles within the vapor layer and accelerating these charged particles against the tissue). As discussed above, the requisite voltage level for ablation will vary depending on the number, size, shape and spacing of the electrodes, the distance in which the electrodes extend from the support member, etc. Once the surgeon places the power supply in the “ablation” mode,voltage level adjustment230 orthird foot pedal239 may be used to adjust the voltage level to adjust the degree or aggressiveness of the ablation.

It will be recognized that the voltage and modality of the power supply may be controlled by other input devices. However, applicant has found that foot pedals are convenient methods of controlling the power supply while manipulating the probe during a surgical procedure.

In the coagulation mode, thepower supply228 applies a low enough voltage to the electrode terminals (or the coagulation electrode) to avoid vaporization of the electrically conductive fluid and subsequent molecular dissociation of the tissue. The surgeon may automatically toggle the power supply between the ablation and coagulation modes by alternatively stepping onfoot pedals237,238, respectively. This allows the surgeon to quickly move between coagulation and ablation in situ, without having to remove his/her concentration from the surgical field or without having to request an assistant to switch the power supply. By way of example, as the surgeon is sculpting soft tissue in the ablation mode, the probe typically will simultaneously seal and/or coagulation small severed vessels within the tissue. However, larger vessels, or vessels with high fluid pressures (e.g., arterial vessels) may not be sealed in the ablation mode. Accordingly, the surgeon can simply step onfoot pedal238, automatically lowering the voltage level below the threshold level for ablation, and apply sufficient pressure onto the severed vessel for a sufficient period of time to seal and/or coagulate the vessel. After this is completed, the surgeon may quickly move back into the ablation mode by stepping onfoot pedal237.

Now referring toFIGS. 3 and 4, an exemplaryelectrosurgical probe300 incorporating anactive screen electrode302 is illustrated.Probe300 may include anelongated shaft304 which may be flexible or rigid, ahandle306 coupled to the proximal end ofshaft304 and anelectrode support member308 coupled to the distal end ofshaft304. Probe300 further includesactive screen electrode302 and securingelectrode303.Return electrode310 is spaced proximally fromscreen electrode302 and provides a method for completing the current path betweenscreen electrode302 and securingelectrode303. As shown,return electrode310 preferably comprises an annular exposed region ofshaft304 slightly proximal ofinsulative support member308, typically about 0.5 to 10 mm and more preferably about 1 to 10 mm. Securingelectrode303 and returnelectrode310 are each coupled torespective connectors328 disposed in handle306 (as illustrated inFIG. 4) that extend to the proximal end ofprobe300, whereconnectors328 are suitably electrically connected to a power supply (e.g.,power supply10 inFIG. 1 orpower supply228 inFIG. 2). As shown inFIG. 4, handle306 defines aninner cavity326 that houses theelectrical connectors328, and provides a suitable interface for connection to an electrical connecting cable (e.g.,cable22 inFIG. 1 orcable234 inFIG. 2).

Still referencingFIGS. 3 and 4, in certainembodiments screen electrode302, securingelectrode303 andinsulative support member308 are configured such thatscreen electrode302 and securingelectrode303 are positioned on a lateral side of the shaft304 (e.g., 90 degrees from the shaft axis) to allow the physician to access tissue that is offset from the axis of the portal or arthroscopic opening into the joint cavity in which theshaft304 passes during the procedure. To accomplish this, probe300 may include an electricallyinsulating cap320 coupled to the distal end ofshaft304 and having alateral opening322 for receivingsupport member308,screen electrode302, and securingelectrode303.

Shaft304 preferably comprises an electrically conducting material, usually metal, which is selected from the group consisting of tungsten, stainless steel alloys, platinum or its alloys, titanium or its alloys, molybdenum or its alloys, and nickel or its alloys.Shaft304 may include an electrically insulatingjacket309, which is typically formed as one or more electrically insulating sheaths or coatings, such as polytetrafluoroethylene, polyimide, and the like. The provision of the electrically insulating jacket over the shaft prevents direct electrical contact between these metal elements and any adjacent body structure or the surgeon. Such direct electrical contact between a body structure and an exposed electrode could result in unwanted heating and necrosis of the structure at the point of contact causing necrosis.

Theprobe300 further includes asuction connection tube314 for coupling to a source of vacuum, and an inner suction lumen312 (FIG. 4) for aspirating excess fluids, tissue fragments, and/or products of ablation (e.g., bubbles) from the target site. Preferably,connection tube314 andsuction lumen312 are fluidly connected, thereby providing the ability to create a suction pressure inlumen312 that allows the surgeon to draw loose tissue, e.g., synovial tissue, towards thescreen electrode302. Typically, the vacuum source is a standard hospital pump that provides suction pressure toconnection tube314 andlumen312. As shown inFIGS. 3 and 4,internal suction lumen312, which preferably comprises peek tubing, extends fromconnection tube314 inhandle306, throughshaft304 to anaxial opening316 insupport member308, throughsupport member308 to alateral opening318 insupport member308.Lateral opening318 is positioned adjacent toscreen electrode302, which further includes a suction port (not shown) disposed on the surface ofscreen electrode302 and fluidly connected tolateral opening318 for allowing aspiration therethrough, as discussed below in more detail.

FIG. 5 representatively illustrates in more detail the removal of a target tissue by use of an embodiment ofelectrosurgical probe50 according to the present disclosure. As shown, the high frequency voltage is sufficient to convert the electrically conductive fluid (not shown) between thetarget tissue502 and active electrode terminal(s)504 into an ionizedvapor layer512 or plasma. As a result of the applied voltage difference between electrode terminal(s)504 and the target tissue502 (i.e., the voltage gradient across the plasma layer512), chargedparticles515 in the plasma are accelerated. At sufficiently high voltage differences, these chargedparticles515 gain sufficient energy to cause dissociation of the molecular bonds within tissue structures in contact with the plasma field. This molecular dissociation is accompanied by the volumetric removal (i.e., ablative sublimation) of tissue and the production of lowmolecular weight gases514, such as oxygen, nitrogen, carbon dioxide, hydrogen and methane. The short range of the accelerated chargedparticles515 within the tissue confines the molecular dissociation process to the surface layer to minimize damage and necrosis to theunderlying tissue520.

During the process, thegases514 will be aspirated through a suction opening and suction lumen to a vacuum source (not shown). In addition, excess electrically conductive fluid, and other fluids (e.g., blood) will be aspirated from thetarget site500 to facilitate the surgeon's view. During ablation of the tissue, the residual heat generated by the current flux lines510 (typically less than 150° C.) betweenelectrode terminals504 and returnelectrode511 will usually be sufficient to coagulate any severed blood vessels at the site. If not, the surgeon may switch the power supply (not shown) into the coagulation mode by lowering the voltage to a level below the threshold for fluid vaporization, as discussed above. This simultaneous hemostasis results in less bleeding and facilitates the surgeon's ability to perform the procedure. Once the blockage has been removed, aeration and drainage are reestablished to allow the sinuses to heal and return to their normal function.

Now referring toFIG. 6, the distal end portion of a preferred embodiment of an electrosurgical probe according to present disclosure is shown.Electrosurgical probe600 comprisesactive screen electrode602 mounted to insulativesupport member604 disposed at a distal end ofelongate shaft601. Probe600 also includes electricallyinsulating cap612 coupled to the end ofshaft601 and configured to receivescreen electrode602 andsupport member604. In preferred embodiments, securingelectrode606 extends throughscreen electrode602 andsupport member604 to mechanicallysecure screen electrode602 to supportmember604 and electricallyinsulating cap612. In certain configurations, securingelectrodes606 may be characterized byhead607,leg608, andtab610. Preferably,head607 contacts or engages the superior surface ofscreen electrode602, thereby providing an electrical means for the transmission of RF energy between securingelectrode606 andscreen electrode602.Support member604 may be characterized bychannel609 andslot611, whereinchannel609 is oriented perpendicularly with respect to the axis ofshaft601 andslot611 is oriented axially with respect to the axis ofshaft601.Wire613 extends proximally fromslot611, and is electrically connected to the electrical connectors disposed in the handle of the probe (as discussed above).Return electrode614 is spaced proximally fromscreen electrode602. As discussed above, in thisembodiment screen electrode602 andsupport member604 are configured such thatscreen electrode602 is positioned on the lateral side of shaft601 (e.g.,90 degrees from the shaft axis) to allow the physician to access tissue that is offset from the axis of the port or arthroscopic opening into the joint cavity in whichshaft601 passes during the procedure.

Referring now toFIG. 7A, an embodiment of securingelectrode606 is shown. Securingelectrode606 may be formed with a conductive material such as tungsten, and the shape and profile of securingelectrode606 may be manufactured via etching, laser cutting, or injection molding. In certain configurations, securingelectrode606 may be characterized bysaw tooth pattern615 on the superior plasma forming surface of securingelectrode606. The added edges formed on securingelectrodes606 bysaw tooth pattern615 in this configuration may result in increased current density and thus promote the formation of improved zones for plasma formation and RF ablation.

Referring now toFIG. 7B,screen electrode602 will comprise a conductive material, such as tungsten, titanium, molybdenum, stainless steel, aluminum, gold, copper or the like.Screen electrode602 will usually have a diameter in the range of about 0.5 to 8 mm, preferably about 1 to 4 mm, and a thickness of about 0.05 to about 2.5 mm, preferably about 0.1 to 1 mm.Screen electrode602 may have a variety of different shapes, such as the shape shown inFIG. 7B. Screen electrode may haveslots616 therethrough, and may comprisesuction opening618 having sizes and configurations that may vary depending on the particular application.Suction opening618 will typically be large enough to allow ablated tissue fragments to pass through into suction lumen port620 (seeFIG. 8), typically being about 2 to 30 mils in diameter, preferably about 5 to 20 mils in diameter. In some applications, it may be desirable to only aspirate fluid and the gaseous products of ablation (e.g., bubbles) so that the holes may be much smaller, e.g., on the order of less than 10 mils, often less than 5 mils. In certain configurations,suction opening618 may be formed in the shape of a zigzag or lightning bolt.

Referring now toFIG. 8, insulativeelectrode support member604 preferably comprises an inorganic material, such as glass, ceramic, silicon nitride, alumina or the like, that has been formed with lateral and axialsuction lumen openings620,622, and with one or more lateralaxial passages624 for receivingelectrical wires613.Wires613 extend from electrical connectors (i.e.,electrical connectors328 inFIG. 4), throughshaft601 andpassages624 insupport member604, terminating in proximity toslots611 andtabs610 of securingelectrodes606.Wires613 are electrically connected to securing electrodes606 (e.g., by a laser welding process) thereby electrically coupling securingelectrodes606 andscreen electrode602 to a high frequency power supply. Referring toFIGS. 6,7B, and8,legs608 may extend throughslots616 ofscreen electrode602 andchannels609 ofsupport member604, andtabs610 may be inserted intoslots611 ofsupport member604 such thattabs610 interfere or engage with a portion ofsupport member604. The placement of securingelectrodes606 such thattabs610 are inserted intoslots611 creates a mechanical method of joining securingelectrodes606 to supportmember604 and thereby prevents securingelectrodes606 from moving axially with respect toshaft601 andsupport member604. Additionally, the method of mechanical securement results in the capture ofscreen electrode602 between securingelectrodes606 andsupport member604. Further, as described above the contact betweenheads607 of securingelectrodes606 andscreen electrode602 provides a method to electrically transmit RF energy throughsupport member604 toscreen electrode602.

In additional embodiments, the mechanical method of joining may comprise complementary helical threads cut inchannels609 ofsupport member604 and respectively inlegs608 of securingelectrodes606, whereinlegs608 of securingelectrodes606 are operable to threadingly engagechannels609 ofsupport member604. Additional embodiments of the present disclosure may include configurations wheretabs610 are formed in a barb or arrowhead shape and are disposed in interference withsupport member604. Moreover, inadditional embodiments tabs610 may be completely enclosed withinsupport member604, and may be further secured to supportmember604 by epoxy.

Referring now toFIGS. 9 and 10, the distal end portion ofrepresentative probe600 is shown with at least twobilateral securing electrodes606 thereon. In this configuration, securingelectrodes606 may be oriented symmetrically about the central axis ofshaft601, and may thereby allow for creation of a zone for RF ablation orplasma chamber1000 between the symmetrically oriented bilateral securingelectrodes606 as well as between securingelectrodes606 and screen electrode602 (see i.e.,FIG. 10). Incorporation ofsymmetrical securing electrodes606 may allow for the creation of a three dimensional zone represented byplasma zone1000 for carrying out RF ablation.

Other modifications and variations can be made to disclose embodiments without departing from the subject invention as defined in the following claims. For example, it should be noted that the invention is not limited to an electrode array comprising a plurality of electrode terminals. The invention could utilize a plurality of return electrodes, e.g., in a bipolar array or the like. In addition, depending on other conditions, such as the peak-to-peak voltage, electrode diameter, etc., a single electrode terminal may be sufficient to contract collagen tissue, ablate tissue, or the like.

In addition, the active and return electrodes may both be located on a distal tissue treatment surface adjacent to each other. The active and return electrodes may be located in active/return electrode pairs, or one or more return electrodes may be located on the distal tip together with a plurality of electrically isolated electrode terminals. The proximal return electrode may or may not be employed in these embodiments. For example, if it is desired to maintain the current flux lines around the distal tip of the probe, the proximal return electrode will not be desired.

While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching herein. The embodiments described herein are exemplary only and are not limiting. Because many varying and different embodiments may be made within the scope of the present teachings, including equivalent structures or materials hereafter thought of, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.

Claims (15)

What is claimed is:

1. An electrosurgical instrument for removing tissue from a target site within or on a patient's body comprising:

a shaft having a proximal end and a distal end portion;

an electrode assembly comprising a substantially flat active screen electrode positioned on the distal end portion of the shaft, at least one return electrode positioned on the shaft and spaced away from the active electrode, and at least one securing electrode positioned on the distal end portion of the shaft and disposed through a screen slot in the screen electrode, the at least one securing electrode comprising an electrode head that electrically connects the at least one securing electrode to the screen electrode;

wherein the at least one securing electrode further comprises a leg extending from the electrode head, and a tab extending from the leg;

an electrically insulating support member upon which the screen electrode is mounted, the support member mechanically interfering with and engaging a portion of the tab of the at least one securing electrode, wherein the electrode head has an elongate surface extending beyond the screen slot such that the combination of the electrode head and the tab mechanically act to fixedly secure the screen electrode to the support member and maintain electrical connection between the at least one securing electrode and the screen electrode; and

at least one electrical connector extending through the shaft, wherein the at least one securing electrode is electrically coupled to the at least one electrical connector at the tab.

2. The instrument ofclaim 1, wherein the tab mechanically engages a corresponding axial slot disposed along an outer surface of the support member.

3. The instrument ofclaim 2, wherein the leg is received within a corresponding channel disposed along the outer surface of the support member.

4. The instrument ofclaim 3, wherein the electrode head engages a superior surface of the active screen electrode, and the leg is received into the corresponding channel through the screen electrode slot.

5. The instrument ofclaim 1, the at least one securing electrode having a saw tooth pattern on a superior surface.

6. The instrument ofclaim 1 further comprising an aspiration lumen within the shaft having a distal opening coupled to the screen electrode to inhibit clogging of the lumen, wherein the support member has an axial opening in communication with the lumen and a lateral opening in contact with the screen electrode.

7. The instrument ofclaim 1 wherein the screen electrode and the at least one securing electrode are configured to be brought adjacent a tissue structure immersed in electrically conductive fluid and the electrically conductive fluid completes a conduction path between the screen electrode, the at least one securing electrode and the return electrode.

8. The instrument ofclaim 7, wherein upon the application of a sufficiently high frequency voltage between the screen electrode, the at least one securing electrode, and the return electrode the conductive fluid vaporizes in a thin layer over at least a portion of the screen electrode and the at least one securing electrode and induces the discharge of energy from the vapor layer.

9. The instrument ofclaim 8 wherein the discharge of energy from the vapor layer is sufficient to form a plasma.

10. The instrument ofclaim 8, wherein the vapor layer is configured to contact the tissue structure and is capable of ablating a portion of the tissue structure.

11. An electrosurgical instrument for removing tissue from a target site within or on a patient's body comprising:

a shaft having proximal and distal end portions;

an electrode assembly on the distal end portion, the electrode assembly comprising a substantially flat active screen electrode, a return electrode spaced from the active screen electrode, and bilateral securing electrodes electrically coupled to the active screen electrode and securing the active screen electrode to the shaft;

wherein each securing electrode comprises an electrode head, a leg extending from the head and a tab extending from the leg, wherein the electrode head has an elongate surface that engages and secures the screen electrode, and wherein the electrode head electrically connects each securing electrode to the screen electrode;

an insulative support body operable to support the active screen electrode and engage the tabs of the bilateral securing electrodes so as cooperate with the electrode head to mechanically secure the screen electrode to the support body; and

electrical connectors extending through the shaft, the electrical connectors operable to couple the bilateral securing electrodes with a high frequency power supply.

12. The instrument ofclaim 11 wherein the tabs engage axial slots in the support body.

13. The instrument ofclaim 11 wherein the bilateral securing electrodes each have a superior surface characterized by a plurality of teeth.

14. The instrument ofclaim 11, wherein the bilateral securing electrodes are disposed in a symmetric orientation to one another about a central axis of the shaft.

15. The instrument ofclaim 14, wherein the symmetric orientation of the bilateral securing electrodes defines a plasma chamber between the bilateral securing electrodes.

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